This application relates to a method of coating fibers mixed into a plastic matrix, such that the fibers do not begin to cure, or react with the matrix until the coating is broken, just prior to the matrix/fibers being delivered into a mold.
Plastics with incorporated reinforcement fibers are widely utilized in many molding operations. The fiber provides strength to the molded part. As molded parts are becoming more prevalent for more challenging applications, the use of the fiber reinforced plastic also becomes more prevalent.
As the fiber pieces are mixed into a plastic matrix, the plastic matrix is absorbed by the fibers, and in the process, the fibers will expand and displace more volume. With this expansion, viscosity increases dramatically. The mixture quickly becomes very difficult to move. It is typical that the various components being delivered into a injection mold are delivered by pumps from storage canisters. If the fibers and the plastic matrix have been mixed for any length of time, the mixture is often too thick to move by standard pumps. Thus, it is typical that the fiber is mixed into the plastic matrix at the location of the molding, and shortly before molding begins. While this has proven acceptable, it does put restraints on pre-mixing of the fiber and plastic, and further requires that any location where one wishes to injection mold fiber-reinforced plastics must also be provided with a fiber/plastic matrix mixing facility. Mixing of the fiber and plastic is a somewhat challenging application in that the fibers can mix into the surrounding air. Thus, methods of segregating and cleaning the air in the mixing room are required. As can be appreciated, this places further restrictions on where injections molding of fiber-reinforced plastics can occur. A local, and expensive, mixing room is required.
In a disclosed embodiment of this invention, glass fibers are coated with a coating that prevents the fiber from absorbing with a plastic matrix. The coated fibers are then mixed into the plastic matrix. Since the coating prevents the absorption, the fibers can be mixed into the plastic matrix and then transported to a molding location. Thus, the restrictions as mentioned above are eliminated. The plastic matrix including the coated fibers is passed through a mixing station on the way to a mold. The mixing station is preferably provided with rotating screw members which crack the coating. Once the coating is cracked or otherwise broken, then the absorption as mentioned above will begin. However, the mixed plastic and fibers are then being immediately delivered to the mold. The absorption is as intended, rather than complicating the transportation of the mixture.
In preferred embodiments, the coating of the glass fibers is of a SILANE(trademark), or an epoxy, or a combination of the two. However, any type of coating which will delay the fiber being able to absorb the plastic matrix would be within the scope of this invention. Particular coating agents include epoxylated phenolics, epoxylated carboxylic acids, polymers of unsatured epoxides, epoxidated dienes or polyenes, and mixtures of any of the foregoing. The above are examples of thermo set coating. Also, polystyrene thermoplastics may be used as one example.
The fibers are preferably glass fibers or strands. The invention may also be used on filamentary materials such as thermoplastic synthetic fibers like polyesters, nylons and cellulous acetate. Preferably the coating is applied after the formation of the fibers, and while the fibers are in the forms of strands, yarns or rovings. The glass fibers may be any glass fiber produced from fiberizable heat-softened glass. Examples include well known fiberizable glass compounds like xe2x80x9cE-glassxe2x80x9d and xe2x80x9c621-glassxe2x80x9d. Also, other acceptable derivatives of xe2x80x9cE-glassxe2x80x9d and xe2x80x9c621-glassxe2x80x9d can be used such as low or free-floating and/or boron fiberizable glass compositions.
The length of the glass filaments and whether or not they are bundled into fibers and the fibers bundled in turn to yarns, ropes or rovings is not critical to this invention. Moreover, the composition of the plastic matrix while perhaps important to the molding of any particular item, is not critical to the coating and storing aspects of this invention.
While glass fibers are preferably utilized, other reinforcements including carbon fibers, aramid fibers, KEVLAR, polyesters and the like, and even wood or other organic fibers can benefit from this invention.
The exact details and methods for forming the coated fibers are best understood from co-pending patent application, Ser. No. 09/829,095, filed Apr. 9, 2001, assigned to the assignee of the present application, and entitled xe2x80x9cCoated Fibers and Processxe2x80x9d and naming the inventor Jay Bellasalma, who is also an inventor of the present application.
The coated fibers are premixed into a plastic matrix, and may then be stored in a storage container such as is commonly used for the plastic matrix. These containers can then be transported to a molding location. In this way, a single location can be used for the mixing of the fiber and plastic matrix for a plurality of molding locations. Once at the molding location, the material is moved from the container through the mixing head and into the mold. As mentioned above, the mixing head will crack the coating, and allow the fibers to begin to absorb the matrix.
The present invention minimizes the complexity and requirement for specific xe2x80x9cmixing roomsxe2x80x9d and the like as exist today. With this invention, fibers may be mixed into the plastic matrix, and stored. The fibers may thus be mixed into the plastic matrix at a location remote from the molding station. In this way, the mixing rooms which require complex air treatment systems need not be provided at every location where molding is to occur. Rather, pre-mixed plastic matrix and fiber may be shipped to molding locations remote from the mixing location. This simplifies the use of fiber-reinforced plastic for molding purposes.
One structure for moving the plastic is disclosed in U.S. patent application Ser. No. 09/662,302 entitled xe2x80x9cRapid Discharge Multiple Material Delivery Systemxe2x80x9d and filed on Sep. 15, 2000. One structure of the preferred mixing head is disclosed in co-pending patent application Ser. No. 09/662,662 now U.S. Pat. No. 6,536,936 entitled xe2x80x9cMix Head Assembly For a Molding Material Delivery Systemxe2x80x9d and filed on Sep. 15, 2000.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.